I’m a Computer Science/Math PhD who qualified for two Olympic trials during my 5.5 years at Caltech.
In my opinion, the flexibility of a PhD work schedule can work pretty well with training. That being said, it’s far from ideal: deadlines for paper submission hit hard and you sometimes have to travel quite a bit to present work.
It’s also a pretty obsessive endeavor. The only recognition you get from your friends and family is usually “wow PhD,” much like the “wow marathon” reactions you get for running. The drive to do a GOOD PhD is like the drive to run a good marathon — it’s mostly internal. It can be hard to keep the fire going on both sides.
With regards to Maia, I think it’s weird to judge her decision or topic of study. A lot of people go into PhDs for the wrong reasons, but there’s no reason to believe this is the case here. Humanities PhD programs are extremely limited — if Harvard professors are writing letters of recommendation for her I trust they know better than us.